As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each user) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
The third generation partnership project long term evolution (“3GPP LTE”) is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications. The improvements are being made to cope with continuing new requirements and the growing base of users. Goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards. The project envisions a packet switched communications environment with support for such services as VoIP (“Voice over Internet Protocol”). The 3GPP LTE project is not itself a standard-generating effort, but will result in new recommendations for standards for the UMTS.
The UTRAN includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). However, it should be noted that the RNC may not be present in the actual implemented systems incorporating Long Term Evolution (LTE) of UTRAN (E-UTRAN). LTE may include a centralized or decentralized entity for control information. In UTRAN operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to Global System for Mobile Communications (GSM) base stations. In E-UTRAN systems, the e-Node B may be, or is, connected directly to the access gateway (“aGW,” sometimes referred to as the services gateway “sGW”). Each Node B may be in radio contact with multiple UEs (generally, user equipment including mobile transceivers or cellphones, although other devices such as fixed cellular phones, mobile web browsers, laptops, PDAs, MP3 players, gaming devices with transceivers may also be UEs) via the radio Uu interface.
The wireless communication systems as described herein are applicable to, for instance, 3GPP LTE compatible wireless communication systems and of interest is an aspect of LTE referred to as “evolved UMTS Terrestrial Radio Access Network,” or E-UTRAN. In general, E-UTRAN resources are assigned more or less temporarily by the network to one or more UEs by use of allocation tables, or more generally by use of a downlink resource assignment channel or physical downlink control channel (PDCCH). LTE is a packet-based system and, therefore, there may not be a dedicated connection reserved for communication between a UE and the network. Users are generally scheduled on a shared channel every transmission time interval (TTI) by a Node B or an evolved Node B (e-Node B). A Node B or an e-Node B controls the communications between user equipment terminals in a cell served by the Node B or e-Node B. In general, one Node B or e-Node B serves each cell. A Node B may be sometimes referred to as a “base station.” Resources needed for data transfer are assigned either as one time assignments or in a persistent/semi-static way. The LTE, also referred to as 3.9G, generally supports a large number of users per cell with quasi-instantaneous access to radio resources in the active state. It is a design requirement that at least 200 users per cell should be supported in the active state for spectrum allocations up to 5 megahertz (MHz), and at least 400 users for a higher spectrum allocation.
In order to facilitate scheduling on the shared channel, the e-Node B transmits a resource allocation to a particular UE in a downlink-shared channel (PDCCH) to the UE. The allocation information may be related to both uplink and downlink channels. The allocation information may include information about which resource blocks in the frequency domain are allocated to the scheduled user(s), the modulation and coding schemes to use, what the size of the transport block is, and the like.
The lowest level of communication in the E-UTRAN system, Level 1, is implemented by the Physical Layer (“PHY”) in the UE and in the e-Node B and the PHY performs the physical transport of the packets between them over the air interface using radio frequency signals. In order to ensure a transmitted packet was received, an automatic retransmit request (“ARQ”) and a hybrid automatic retransmit request (“HARQ”) approach is provided. Thus whenever the UE receives packets through one of several downlink channels, including command channels and shared channels, the UE performs a communications error check on the received packets, typically a Cyclic Redundancy Check (CRC), and in a later sub-frame following the reception of the packets, transmits a response on the uplink to the e-Node B or base station. The response is either an Acknowledge (ACK) or a Not Acknowledged (NACK) message. If the response is a NACK, the e-Node B automatically retransmits the packets in a later sub-frame on the downlink or DL. In the same manner, any UL transmission from the UE to the e-Node B is responded to, at a specific sub-frame later in time, by a NACK/ACK message on the DL channel to complete the HARQ. In this manner, the packet communications system remains robust with a low latency time and fast turnaround time.
E-UTRAN networks may provide VoIP (Voice over Internet Protocol) support. To provide this support, the UE may transmit to the e-Node B over the air interface packets at a predetermined timing interval, so that the voice signals that are eventually formed from these VoIP packets are free of jitter and noise that would otherwise result. Semi-persistent scheduling (“SPS”) may be used to allocate uplink (UL) physical resource blocks (PRBs) to ensure the VoIP packets are delivered at appropriate intervals to maintain quality of service and reduce control signaling cost. The need to provide UL packets from the UE to the e-Node B has certain impacts on other aspects of the operations of the physical layer, including retransmit requests and synchronous HARQ processes that result from previous UL packet transmissions that were not received by the e-Node B. A UE may have a transmission conflict between a scheduled UL resource such as an initial transmission for a VoIP packet and a need to service a HARQ retransmission request packet at the appropriate time.
A continuing need thus exists for a system, methods and circuitry to implement support for certain persistently scheduled services that have predetermined timing requirements in the E-UTRAN system, while avoiding collisions with retransmission requests, without the need for additional communications from higher layers or burdening other radio resources.